I came across the book "Singapore Stamps: Anniversaries & Milestones" and found it to be a good read. The authors (Tan Wee Kiat, Ivan Chew and Ong Yew Ghee) have taken pain to research and compile the many stories behind the diferent stamps issues.
Some stories had me taking another look at some stamps in my own collection. For example, the authors highlighted that the design of the 1969 issue on Public Housing has a 100,000 homes in the form of a '1' and many '0's stacked like a HDB flat.
There are many other books in this series of Singapore stamps, and the books are available from the library for those who want to take a quick look.